Diesel engines, preferred for transportation due to high durability and efficiency, suffer from the undesired emission of harmful soot particles. The available technologies to reduce particulate emissions such as diesel particulate filters are less readily used due to the costs associated with them. Thus, novel and inexpensive method to reduce their emissions is desired. This paper presents a new hydrocarbon-based additive, dicyclopentadiene (DCPD), for diesel fuel that is shown to reduce the particulate emissions, while enhancing the cetane number for diesel. The sooting tendency of diesel blended with DCPD is studied by determining the smoke points, and the optimum blending ratio to minimize soot emissions is reported. The effect of DCPD addition on soot morphology and reactivity is also studied using different characterization techniques such as X-ray diffraction and high-resolution transmission electron microscopy for the nanostructural changes, and elemental analysis, thermogravimetric analysis, electron energy loss spectroscopy, and Fourier transform infrared for the variation in their reactivity and chemical properties. The oxidative kinetics of soots from blended fuel and pure diesel are also calculated. The results indicate that a small fraction of DCPD in diesel could act as a cetane improver, minimize soot production, and improve the physicochemical properties of soot by making it highly reactive in air to reduce its lifetime in the environment.